Thrombin is a serine protease present in blood plasma in the form of a precursor, pro-thrombin. Thrombin has been known for growth-promoting activity for a wide variety of cells from various tissues by activation of a specific cell surface receptor known as the non-proteolytically activated thrombin receptor. For example, thrombin has been shown to promote angiogenesis, the development of new blood vessels, and to stimulate endothelial cell proliferation (see, e.g., U.S. Pat. Nos. 5,352,664, 5,500,412, the contents of which are incorporated herein by reference in its entirety).
Thrombin peptide derivatives are synthetic analogs of thrombin which have an amino acid sequence derived at least in part from that of thrombin and are active at the non-proteolytically activated thrombin receptor. For example, thrombin peptide derivatives from amino acids 508-530 of human pro-thrombin have been described by the present inventors for promoting thrombin receptor mediated cell stimulation and for repair, and promoting cardiac tissue repair (see, e.g., U.S. Pat. Nos. 5,352,664, 5,500,412, WO 02/07748, WO 02/005836, WO 02/004008 and WO 03/013569, the contents of which are incorporated herein by reference in their entirety).
Thrombin peptide derivatives show great potential as pharmaceuticals because of their therapeutic activity for the treatment of wounds, stimulating bone growth and cartilage growth and promoting cardiac repair. Unfortunately, however, thrombin peptide derivatives are highly susceptible to dimerization. For example, TP508, an example of a thrombin peptide derivative having the amino acid sequence H-Ala-Gly-Tyr-Lys-Pro-Asp-Glu-Gly-Lys-Arg-Gly-Asp-Ala-Cys-Glu-Gly-Asp-Ser-Gly-Gly-Pro-Phe-Val-NH2 (SEQ ID NO: 4), dimerizes over time, and has a half-life of about 2 to about 4 hours in certain buffered solutions at neutral pH and a half-life of about 7 days at high peptide concentrations in sterile saline (See Example 1).
It therefore is necessary to develop methods to maintain the purity of thrombin peptide derivatives over extended time periods and prevent or reduce dimerization, so that thrombin peptide derivatives have a long storage life and it is possible to deliver precise and reproducible dosages, even after storage for prolonged periods of time.